Fixes, fail testing:

Core:

* Test buffer_cat iterator move members

HTTP:

* Fixed yield / resume in writer
* Fixed message serialization with chunked encoding

* Test yield / resume in writer
* Test all conditional branches during message serialization
* Test chunked encoding
* Increase coverage on parse_error
* Add parse_error::general

WebSocket:

* Add error::general
* Increase coverage in error

test/websocket/error.cpp

@@ -42,6 +42,7 @@ public:
         check("websocket", error::request_malformed);
         check("websocket", error::request_invalid);
         check("websocket", error::request_denied);
+        check("websocket", error::general);
     }
 };